Positive displacement compressors are widely used in refrigerant compressor applications. One known type, a scroll compressor, includes compression elements and an electric motor disposed within a sealed compressor shell. A quantity of lubricant is also received in the compressor shell. In such compressors, the refrigerant passes over the motor on its way to the inlet of the compression elements, cooling the motor.
At start-up, the oil located in the compressor's sump may contain a quantity of fluid, such as a liquid refrigerant. At start-up, the sump and the motor are cool, and pre-heating does not occur. Therefore, idle compressors often accumulate liquid refrigerant and/or oil in the compression pocket and in the suction plenum. Because the fluids are incompressible, detrimental forces can result if the compressor is rapidly started.
Electric heaters are occasionally used to pre-heat the compressor and thus reduce the amount of accumulated fluid present at start-up. However, this approach has numerous issues. Use of electric heaters adds cost and complexity to the system, and it is ineffective on expelling oil, to name only two examples. Another approach used to prevent accumulation of fluid involves the addition of valves to isolate the compressor during off periods. This approach also adds cost, and adds detrimental stress cycles to the motor and valves. There is therefore a need for a method to remove accumulated fluids from a compressor's compression chamber before operational start-up.